Flashing light systems



Dec. 3, 1963 R. F. BREESE EI'AL 3,113,293

FLASHING LIGHT SYSTEMS Filed Nov. 8, 1961 2 Sheets-Sheet 2 INVENTOEober/ fin/ey Breese BY rf/berf C Faye/fa A TTORNE YS United StatesPatent 3,113,293 FLASH-KING LIGHT SYSTEMS Robert Finley lireese andAlbert C. Zagotta, Chicago, Ill., assiguors to Chicago, Rock Island andPacific Railroad Company, Chicago, 111., a corporation of Delaware FiledNov. 8, 1961, Ser. No. 151,072 16 Claims. (Cl. 340-50) This inventionrelates to flashing light systems and more particularly to systemsusable in railroad applications for warning and signalling purposes andon the front or rear of a train or at highway crossings. The systems ofthis invention are rugged and reliable in operation, can withstandshocks, vibrations and wide temperature changes, and they requireminimum lamp replacement and maintenance. At the same time, the systemsare very compact, are relatively inexpensive in construction, and arereadily installed.

Heretofore, many flashing lights for railroad applica tions have been ofthe type wherein a lamp or a reflector is mounted for rotational orswinging movement to obtain a flashing effect where observed from adistance. The mechanical drives of such systems have not been entirelysatisfactory, and the maintenance costs thereof have been high. Systemshave also been used wherein the lamps have been mounted in fixedposition, and relays have been used to periodically energize the same,but the contacts of such relays burn out rapidly, to create a safetyproblem and to require excessive maintenance.

This invention was evolved with the general object of overcoming thedisadvantages of such prior art systems. According to this invention, anincandescent lamp is periodically energized by a solid state electroniccircuit which is extremely rugged a .d reliable in operation and yetcomparatively simple and inexpensive in design.

An important feature of the invention is in the use of siliconcontrolled rectifiers which have a long life, can withstand severeshocks and vibrations and wide temperature variations, and they have alow internal resistance and can handle large currents. Certain problems,however, are introduced by the use of such rectifiers and furtherfeatures of the invention relate to circuits for overcoming suchproblems.

Another important feature relates to the provision of circuitarrangements for minimizing the effect of wide variations in powersupply voltage, such as are experienced in railroad operation.

A further feature of the invention relates to a circuit arrangement forenergizing a plurality of lamps pointed in different directions, in amanner such as to obtain the same effect as obtained by a swinging lampor reflector.

These and other objects, features and advantages of the invention willbecome more fully apparent from the following detailed description takenin conjunction with the accompanying drawings which illustrate preferredembodiments and in which:

FIGURE 1 is a side elevational view of a rear end portion of a railroadobservation car, showing the positioning of one form of signalling lightin a system of the present invention;

FIGURE 2 is a schematic diagram of a circuit for energizing a light suchas the light of FIGURE 1;

FIGURE 3 is a side elevational view of a forward end portion of arailroad locomotive, showing the positioning of a signal lightarrangement constructed according to this invention;

FIGURE 4 is a front elevational view, on an enlarged scale, of thesignal light on the locomotive of FIGURE 3;

FlGURE 5 is a sectional view taken substantially along line VV of FlGURE4; and

FEGURE 6 is a schematic diagram of a circuit for energizing the lampsystem of FIGURES 35.

Referring to FIGURE 1, reference numeral ltl generally designates asignal light unit shown mounted on the rear end of an observation car 11of a passenger train. The unit 111 includes a stationary lamp 12 whichis periodically energized through the circuit shown in FIGURE 2. A flashrepetition rate of approximately 62 flashes per minute is a convenientrate, but much slower or much higher rates may be used.

To periodically energize the lamp 12, one terminal thereof is connectedto a circuit point 13 which is connected through a silicon controlledrectifier 14 to a negative bus 15 which is connected to the negativeterminal 16 of a power supply 17. The other terminal of the lamp 12 isconnected to a circuit point 18 which is connected through a voltageadjustment circuit 19 and a fuse 21 to the positive terminal 21 of thepower supply 17. The voltage adjustment circuit 19 serves to maintainthe voltage between the bus 15 and the circuit point 13 Within certainlimits, as will be described hereinafter.

The silicon controlled rectifier 14 is a PNPN device forming thesemi-conductor equivalent of a gas thyratron, and has a control or gateelectrode 22 which forms the equivalent of the grid of a gas thyratron.In operation, with a positive voltage applied to the anode relative tothe cathode, the flow is blocked until a certain forward breakovervoltage is reached. At this point the device goes into a high conductionstate and the voltage thereacross drops to one or two volts. In the highconduction state, the current flow is limited only by the externalcircuit impedance and supply voltage. At anode to cathode voltages lessthan the breakover voltage, the device can be switched into the highconduction mode by a small pulse applied from the gate electrode to thecathode. Once the device is in the high conduction state, it willcontinue conduction indefinitely after removal of the gate signal untilthe anode cur-rent is interrupted or diverted for a short time intervalafter which the device regains its forward blocking capabilities.

To utilize such properties of the silicon controlled rectifier inperiodically energizing the lamp 12, the voltage across the rectifier 14must not exceed the forward breakover voltage and a positive pulse mustbe applied to the gate or control electrode 22 of sufficient amplitudeas to switch the rectifier 14 into its high conduction state. It is alsonecessary to provide means for interrupting or diverting current throughthe rectifier, after the lamp 12 has been energized for the desiredflash time duration.

The voltage adjustment circuit 19 limits the voltage between circuitpoint 18 and the negative bus 15 to thereby limit the maximum voltageacross the rectifier 14 and to thereby aid in preventing a voltageexceeding the breakover voltage. In addition, the maximum voltage acrossthe rectifier 14 is limited by a resistor 23 connected in paralleltherewith. Resistor 23 also serves a very desirable and importantfunction in maintaining a certain current flow through the lamp 12 toprevent the temperature of the lamp filament from dropping below acertain value. This substantially increases the operating life of thelamp 12.

To periodically apply a positive pulse to the gate or control electrode22 of the rectifier 14, a pulse generating circuit is provided whichcomprises a unijunction transistor 24, having a first base electrode 25connected through a resistor 26 to the negative bus 15', a second baseelectrode 27 connected through resistors 28 and 29 to a circuit point 30and an emitter electrode 31 connected through a timing resistor 32 tothe circuit point 30 and through a timing capacitor 33 to the negativebus 15. Circuit point 31) is connected through a resistor 34 to thecircuit point 18 so as to be at a positive potential relative to thenegative bus 15, the positive potential being maintained constant by avoltage regulator in the form of a Zener diode 35 connected betweencircuit point 30 and the bus 15. This voltage regulator is veryimportant in obtaining uniform and stable operation of the timingcircuitry despite supply voltage variations such as encountered inrailroad applications.

In operation, the voltage across timing capacitor 33 graduallyincreases, through current flow through a timing resistor 32, until itexceeds a voltage approximately equal to the voltage of circuit point30, multiplied by the ratio of resistance 26 to the total resistance ofresistors 26, 28 and 29. At this point the unijunction transistor 24conducts heavily to discharge the timing capacitor 33 through theresistor 26 and to develop a positive pulse at the first base electrode25, whereupon the voltage again starts to build up across the timingcapacitor 33. The positive pulse developed at base 25 is applied througha coupling capacitor 36 to the gate electrode of the silicon controlledrectifier 14, a resistor 37 being connected between the gate electrode22 and the negative bus 15.

When a positive pulse is applied to the gate electrode 22, the siliconcontrolled rectifier 14 conducts heavily, to energize the lamp 12. Tothereafter deenergize the lamp 12, after the desired flash timeduration, it is necessary to provide means for interrupting or divertingcurrent through the rectifier. In the circuit of FIGURE 2, such meanscomprise a second silicon controlled rectifier 38 having a cathodeconnected to the negative bus and an anode connected through a resistor39 to the circuit point 18 and through a capacitor 40 to the circuitpoint 13.

When the rectifier 14 conducts to energize the lamp 12, the circuitpoint 13 is placed at a potential close to that of the negative bus 15and the capacitor 49 is gradually charged up through current flowthrough resistor 39, to a polarity as indicated on the drawing. Afterthe lamp 12 has been energized for the desired duration of time, therectifier 38 is then rendered conductive to place its anode at apotential close to that of the negative bus 15. Circuit point 13 (andthe anode of rectifier 14) are then placed at a potential which isnegative relative to that of the bus 15, because of the charge ofcapacitor 40 and the fact that it is not possible to instantaneouslychange the charge of a capacitor. Thus current flow through therectifier 14 is interrupted and another positive pulse must be appliedbefore the rectifier is again rendered conductive. The siliconcontrolled rectifier 38 in this application (FIGURE 1) should preferablynot remain conductive until the rectifier 14 again conducts, and theresistor 35 preferably has a resistance which is high enough to reducesteady state current flow through rectifier 38 to a value less than thatrequired to maintain conduction of the rectifier 38.

A positive pulse is applied to a gate electrode 41 of the rectifier 33at appropriate times by means of a pulse generating circuit including aunijunction transistor 42 having a first base electrode connected to thenegative bus 15 through a resistor 43, a second base electrode connectedto the junction between resistors 28 and 29, and an emitter electrodeconnected through a timing resistor 44 to the circuit point 30 andthrough a timing capacitor 45 to the negative bus 15. The first baseelectrode is also connected through a coupling capacitor 45 to the gateelectrode 41 which is connected through a resistor 47 to the negativebus 15.

The operation of this circuit is synchronized with the operation of thecircuit of transistor 24. In particular, the connection of the secondbase of transistor 42 to the junction of resistors 28 and 29 places itat a higher potential than that of the second base 27 of transistor 24,when both transistors are non-conductive. As a result, the emittervoltage required to trigger transistor 24 is less and it fires first.When transistor 24 fires, the potential of the second base electrode oftransistor 42 drops instantaneously and in proper operation, the emittervoltage thereof is then sufficient to cause it to fire instantaneously.

Thus the firing of the transistors 24 and 42 is simultaneous for allpractical purposes. A pair of positive pulses are thus simultaneouslyapplied to the gates 22 and 41 of the silicon controlled rectifiers 14and 38. When the first pair of pulses is applied, the rectifier 14 isrendered conductive. When the next pair of pulses is applied, there isno direct effect on the rectifier 14 since it is already conductive, butthe rectifier 38 is rendered conductive to cut off the rectifier 14through the capacitor 40. When the next following pair of pulses isapplied, the silicon controlled rectifier 14 is again renderedconductive, and so on. Thus the lamp 12 is energized periodically at arate equal to one half the repetition rate of the pulse generatingcircuits. For example, the pulse generating circuits may be operated atthe rate of 124 per minute, to energize the lamp 12 at the rate of 62fiashes per minute.

As above indicated, the voltage adjustment circuit 19 serves to maintainthe voltage between bus 15 and the circuit point 18 within certainlimits. It is particularly designed for railroad applications where thesupply voltage may be either in a low range of from 32 to 38 volts, orwithin a high range of from 64 to 76 volts. A resistor 48 is connectedbetween circuit point 18 and the power supply terminal 21 and has twoadjustable taps 49 and 5!), tap 49 being connected to the end of theresistor 48 which is connected to the circuit point 18. When the voltageis in the low range, the taps 49 and 59 are connected together through anormally closed contact 51 of a relay 52 which is connected in serieswith a resistor 53 between tap 5t and the power supply terminal 16. Tap50 may then be adjusted to obtain the optimum voltage at circuit point18. When the voltage reaches the high range, the relay is energized todisconnect the taps 49 and 50 and to introduce a higher resistance inthe circuit. Tap 49 may then be adjusted to obtain optimum outputvoltage. The relay 52 is of course energized only in response to avoltage in excess of the highest voltage of the low range and lower thanthe lowest voltage of the high range.

Referring now to FIGURES 3, 4 and 5, reference numeral 55 generallydesignates a signal light unit mounted on the front end of a railroadlocomotive 56, and arranged to produce the same general effect as thesweeping beam produced by a conventional swinging headlight, but withstationary lamps. The illustrated unit 55 comprises a lower lamp 57, anupper lamp 58 spaced above the lamp 57, and two side lamps 59 and 6ddisposed in horizontal alignment on opposite sides of the plane of theaxes of lamps 57 and 5?. The illustrated lamps 57-61) are sealed beamunits mounted in a plate 61 by conventional mounting means. The upperand lower lamps 57 and 58 are arranged to project beams directly forwardfrom the locomotive, while the side lamps 59 and 60 are angularlydisplaced in opposite directions so as to project beams at slight sideangles with respect to the directly forward direction.

FIGURE 6 is a schematic diagram of a circuit for energizing the lampsSL619. This circuit operates cyclically to energize the lower lamp 57and one side lamp 59 during the first half of a cycle and to energizethe upper lamp 58 and the other side lamp 60 during the second half of acycle. To an observer who is approach ing or in the path of the beams,the effect is substantially the same as that produced by the sweepingbeam from a conventional swinging headlight.

The circuit of FIGURE 6 is very similar to that of FIGURE 2 and usesmany of the same components. For convenience, the same referencenumerals, with primes, are applied to those elements or components whichare the same. The circuit of FIGURE 6 diiiers from that of FIGURE 2 inthat lamps 57 and 59 are substituted for the lamp 12 of FIGURE 2, whilelamps 58 and 60 are connected in place of the resistor 39. The lamps 58and 60 are energized for a complete half cycle whereas as above notedthe resistor 39 of FIGURE 2 has a relatively high value so as to starveconduction of the rectifier 38, shortly after it is rendered conductiveto cut off the rectifier 14. To limit the voltage across rectifier 38during periods of non-conduction thereof, a resistor 62 is connected inparallel with the silicon controlled rectifier 3fi. Resistor 62 alsomaintains the lamps 58 and 60 in a dimmed condition in which thetemperature of the filaments thereof does not drop below a certainvalue, to thus prolong the operating life of the lamps.

To insure proper operation of the circuit or" FIGURE 6, a capacitor 63is connected between the positive circuit point 30 and the gateelectrode 41' of the rectifier 38' so as to apply a positive signal tothe gate electrode 41 and cause conduction of the rectifier 38' when thepower supply voltage is initially applied. The capacitor 4%) is thencharged up with a polarity as indicated in FIGURE 6. When the first pairof pulses is developed by the triggering circuits, the rectifier 14' isthen rendered conductive and through the charge of the capacitor 40',the rectifier 38' is rendered non-conductive. The capacitor 40' is thencharged up to a polarity opposite that illustrated, so that when thenext pair of positive pulses are developed by the pulse generatingcircuits, the rectifier 38 is again rendered conductive and therectifier M will be cut oil. If the capacitor 63 were not provided, anoperation might result in which neither rectifier would conduct when thepower was initially applied and in which both rectifiers would be placedin conduction in response to the first pair of pulses developed by thepulse generating circuits, to prevent the capacitor 40' from developingany charge and to prevent any commutating action, so that bothrectifiers would remain continuously in conduction.

By way of illustrative example and not by way of limitation, thefollowing values or types of components may be used:

Reference numeral: Value or type 12, 57-60 150 or 200 watt, 32 Volt. 14,14', 38 Transitron type TCR 1010. 38 Transitron type TCRlOOS. 23, 23',62 ohms, 100 watts. 24, 24', 42, 42' General Electric type 2N49l. 26,26', 43, 43' 56 ohms, /2 watt. 28, 28' 180 ohms, /2 watt. 29, 29' 150ohms, /2 watt. 32, 32', 44, 44' 56,000 ohms, /2 watt. 33, 33', 45, 45 10microfarads, 150 volt. 34, 34 1000 ohms, 10 watt. 35, 35 Transitron typeSV2045. 36, 36, 4d, 45 1 microfarad, 150 volt. 37, 37, 4 7, 47 a. 10,000ohms, /2 watt. 39 2200 ohms, 1 watt. 49, ill 30 microfarads, 150 volt.48, 48' 10 ohms, 200 watts. 52, 52. Vapor, 32 volt. 53, 53 3000 ohms, 10watts. 63 2 microfarads, 150 volts.

It will be appreciated that various modifications or additions may bemade. For example, additional lamps may be connected in parallel withthe illustrated lamps, and additional silicon controlled rectifiers maybe connected in parallel with those illustrated to handle higher power.

It will also be appreciated that the systems of this invention may beused in a variety of applications and the term railroad as used hereinis intended to include all applications similar to those illustrated.

It will be understood that other modifications and variations may beeffected without departing from the spirit and scope of the novelconcepts of this invention.

We claim as our invention:

1. In a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, a first silicon controlled rectifierhaving gate and anode electrodes and having a cathode electrodeconnected to said negative terminal, a lamp connected between said anodeelectrode and said positive terminal, means normally operative tomaintain said gate electrode at a certain potential relative to saidcathode, means for periodically applying a positive pulse signal to saidgate electrode to initiate conduction of said rectifier, a capacitorhaving one terminal connected to said anode electrode, resistance meansconnected between the other terminal of said cappacitor and saidpositive terminal to charge said capacitor while said rectifierconducts, a second silicon controlled rectifier having a gate electrode,a cathode electrode connected to said negative terminal and an anodeelectrode connected to said other terminal of said capacitor, and meansfor applying a positive pulse to said gate electrode of said secondrectifier to interrupt current flow through said first rectifier afterit has conducted for a certain length of time.

2. In a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, a silicon controlled rectifierhaving gate and anode electrodes and having a cathode electrodeconnected to said negative terminal, a lamp connected between said anodeelectrode and said positive terminal, a unijunction transistor having anemitter and first and second base electrodes, first resistance meansconnected between said first base electrode and said ne ative terminal,second resistance means connected between said second base electrode andsaid positive terminal, a timing capacitor connected between saidemitter electrodes and said negative terminal, a timing resistorconnected between said emitter electrode and said positive terminal forcharging said capacitor until said emitter electrode reaches a firingpotential at which said transistor conducts to discharge said capacitorand to develop a positive pulse at said first base electrode thereof,coupling means for applying said positive pulse to said gate electrodeto initiate conduction of said silicon controlled rectifier, and meansfor interrupting current flow through said rectifier after it hasconducted for a certain length of time following each positive pulse.

3. In a signal light system, a semiconductor device having a pair ofmain electrodes and a control electrode for controlling conductionbetween said main electrodes, a lamp having a pair of terminals, meansconnecting one terminal of said lamp to one of said main electrodes,means for connecting the other terminal of said lamp and the other ofsaid main electrodes to a voltage source, means normally operative tomaintain said control electrode at a certain potential relative to theother of said main electrodes, means for periodically applying a signalto said control electrode to cause conduction of said semiconductordevice and to thereby energize said lamp, and a resistor connected inparallel with said semiconductor device to reduce the voltagethereacross so as to prevent conduction of said device while saidcontrol electrode is at said certain potential and to also maintain saidlamp in a dimmed condition.

4. In a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, first and second silicon controlledrectifiers each having gate and anode electrodes, and a cathodeelectrode connected to said negative terminal, first and secondresistance cans respectively connected between said anode electrodes andsaid positive terminal, at least one of said resist-ance means includinga lamp, a commutation capacitor connected between said anode electrodes,first and second unijunction transistors each having emitter and firstand second gate electrodes, third and fourth resistance means connectedbetween said first base electrodes and said negative terminal, fifthresistance means connected in series between said second base electrodeof said first transistor and said positive terminal, sixth resistancemeans connected between said second base electrodes, a pair of timingcapacitors connected between said emitter electrodes and said negativeterminal, a pair of timing resistors connected between said emitterelectrodes and said positive terminal to charge said timing capacitorsuntil said emitter electrode of said second transistor reaches a firingpotential at which said second transistor conducts to then lower thepotential of said second base electrode of said first transistor andinitiate firing thereof, thereby to simultaneously discharge said timingcapacitors and simultaneously develop a pair of pulses at said firstbase electrodes, and means for applying said pulses to said gateelectrodes to initiate conduction of one rectifier and cut oflfconduction through the other.

5. In a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, a silicon controlled rectifierhaving gate and anode electrodes, and a cathode electrode connected tosaid negative terminal, a lamp connected between said anode electrodeand said positive terminal, means for periodically applying a positivepulse to said gate electrode to render said rectifier conductive, meansfor internupting current through said rectifier after it has conductedfor a certain length of time, and a resistor connected in parallel withsaid recti fier to limit the voltage thereacross while it is non-comductive and to maintain said lamp in a dimmed condition.

6. In a railroad flashing light system, negative and positive terminals,means including a series resistor having an adjustable tap forconnecting said terminals to a source of voltage which is either in ahigh range or a low range, a relay arranged to be energized when saidvoltage is in said high range and having a normally closed contactconnecting said tap and one end of said resistor when said relay isdeenergized, a silicon controlled rectifier having gate and anodeelectrodes, and a cathode electrode connected to said negative terminal,a lamp connected between said anode electrode and said positiveterminal, means for periodically applying a positive pulse to said gateelectrode to render said rectifier conductive, and means forinterrupting current through said rectifier after it has conducted for acertain length of time.

7. In a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, a first silicon controlled rectifierhaving gate and anode electrodes and having a cathode electrodeconnected to said negative terminal, a lamp connected between said anodeelectrode and said positive terminal, means normally operative tomaintain said gate electrode at a certain potential relative to saidcathode, means for periodically applying a positive pulse signal to saidgate electrode to initiate conduction of said rectifier, a capacitorhaving one terminal connected to said anode electrode, resistance meansconnected between the other terminal of said capacitor and said positiveterminal to charge said capacitor while said rectifier conducts, asecond silicon controlled rectifier having an emitter electrode, acathode electrode connected to said negative terminal and an anodeelectrode connected to said other terminal of said capacitor, and meansfor applying -a positive pulse to said gate electrode of said secondrectifier to interrupt current flow through said first rectifier afterit has conducted for a certain length of time, said resistance meanshaving a value high enough to starve said second rectifier of currentafter it has conducted to cut oli said first rectifier.

8. In a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, a silicon controlled rectifierhaving gate and anode electrodes and having a cathode electrodeconnected to said negative terminal, a lamp connected between said anodeelectrode and said positive terminal, a unijunction transistor having anemitter and first and second base electrodes, first resistance meansconnected between said first base electrode and said negative terminal,a Zener diode having one terminal connected to said negative terminal,second resistance means connecting the other terminal of said diode tosaid positive terminal, third resistance means connected between saidsecond base electrode and said other terminal of said diode, a timingcapacitor connected between said emitter electrode and said negativeterminal, a timing resistor connected between said emitter electrode andsaid positive terminal for charging said capacitor until said emitterelectrode reaches a firing potential at which said transistor conductsto discharge said capacitor and to develop a positive pulse at saidfirst base electrode, coupling means for applying said positive pulse tosaid gate electrode to initiate conduction of said silicon controlledrectifier, and means for interrupting current flow through saidrectifier after it has conducted for a certain length of time followingeach positive pulse.

9. In a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, first and second silicon controlledrectifiers each having gate and anode electrodes, and a cathodeelectrode connected to said negative terminal, first and secondresistance means respectively connected between said anode electrodesand said positive terminal, at least one of said resistance meansincluding a lamp, a commutation capacitor connected between said anodeelectrodes, first and second unijunction transistors each having emitterand first and second gate electrodes, third and fourth resistance meansconnected between said first base electrodes and said negative terminal,fifth resistance means connected in series between said second baseelectrode of said first transistor and said positive terminal, sixthresistance means connected between said second base electrodes, a pairof timing capacitors connected between said emitter electrodes and saidnegative terminal, a pair of timing resistors connected between saidemitter electrodes and said positive terminal to charge said timingcapacitors until said emitter electrode of said second transistorreaches a firing potential at which said second transistor conducts tothen lower the potential of said second base electrode of said firsttransistor and initiate firing thereof, thereby to simultaneouslydischarge said timing capacitors and simultaneously develop a pair ofpulses at said first base electrodes, means for applying said pulses tosaid gate electrodes to initiate conduction of one rectifier and cut offconduction through the other, and a capacitor connected between saidpositive terminal and the gate electrode of one of said rectifiers toinsure conduction thereof upon initial application of supply voltage.

10. In a railroad flashing light system, negative and positiveterminals, means including a series resistor having an adjustable tapfor connecting said terminals to a source of voltage which is either ina high range or a low range, a relay arranged to be energized when saidvoltage is in said high range and having a normally closed contactconnecting said tap and one end of said resistor when said relay isdeenergized, a silicon controlled rectifier having gate and anodeelectrodes, and a cathode electrode con nected to said negativeterminal, a lamp connected between said anode electrode and saidpositive terminal, means for periodically applying a positive pulse tosaid gate electrode to render said rectifier conductive, means forinterrupting current through said rectifier after it has conducted for acertain length of time, and a resistor connected in parallel with saidrectifier to limit the voltage thereacross while it is non-conductiveand to maintain said lamp in a dimmed condition.

11. In a railroad flashing light system, negative and positive termianlsfor connection to a voltage source, first and second silicon controlledrectifiers each having gate and anode electrodes, and a cathodeelectrode connected to said negative terminal, first and second lampsrespectively connected between said anode electrodes and said positiveterminal, a commutating capacitor connected between said anodeelectrodes, means for periodically applying a pair of synchronizedpulses to said gate electrodes to initiate conduction of one rectifierand thereby cut off conduction through the other, and means mountingsaid lamps to project beams in angularly related directions.

12. In a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, a first silicon controlled rectifierhaving gate and anode electrodes and having a cathode electrodeconnected to said negative terminal, a lamp connected between said anodeelectrode and said positive terminal, means normally operative tomaintain said electrode at a certain potential relative to said cathode,means for periodically applying a positive pulse signal to said gateelectrode to initiate conduction of said rectifier, a capacitor havingone terminal connected to said anode electrode, resistance meansconnected between the other terminal of said capacitor and said positiveterminal to charge said capacitor while said rectifier conducts, asecond silicon controlled rectifier having an emitter electrode, acathode electrode connected to said negative terminal and an anodeelectrode connected to said other terminal of said capacitor, and meansfor applying a positive pulse to said gate electrode of said secondrectifier to interrupt current flow through said first rectifier afterit has conducted for a certain length of time, said resistance meansincluding a econd larnp.

13. in a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, first and second silicon controlledrectifiers each having gate and anode electrodes, and a cathodeelectrode connected to said negative terminal, first and secondresistance means respectively connected between said anode electrodesand said positive terminal, at least one of said resistance meansincluding a lamp, a coinrnutating capacitor connected between said anodeelectrodes, and means for periodically applying a pair of synchronizedpositive pulses to said gate electrodes to initiate conduction of onerectifier and to thereby cut ofi conduction through the other.

14. In a railroad flashing light system, negative and positive terminalsfor connection to a voltage source, first and second silicon controlledrectifiers each having gate and anode electrodes, and a cathodeconnected to said negative terminal, first and second lamps respectivelyconected between said anode electrodes and said positive terminal, acommutating capacitor connected between said anode electrodes, meansnormally operative to maintain each of said gate electrodes at a certainpotential relative to said cathode, means for periodically applying apair of synchronized pulses to said gate electrodes to initiateconduction of one rectifier and thereby cut oil conduction through theother, and a pair of resistors connected in parallel with saidrectifiers to reduce the voltage across each rectifier while it isnon-conductive and to also maintain the associated lamp in a dimmedcondition.

15. In a railroad flashing light system, negative and postive terminalsfor connection to a voltage source, first and second silicon controlledrectifiers each having gate and anode electrodes, and a cathodeelectrode connected to said negative terminal, first and second resisance means respectively connected between said anode electrodes and saidpositive terminal, at least one of said resistance means including alamp, a coinrnutating capacitor connected between said anode electrodes,means for periodically applying a pair of synchronized positive pulsesto said gate electrodes to initiate conduction of one rectifier and tothereby cut off conduction through the other, and a capacitor connectedbetween said positive terminal and the gate electrode of one of saidrectifiers to insure conduction thereof upon initial application ofsupply voltage.

16. In a railroad flashing light system, first and second lamps arrangedto project a pair of beams in one direction, third an fourth lampsarranged to project beams at one side and the other of said pair ofbeams and at opposite angles relative thereto, negative and positiveterminals for connection to a voltage source, first and second siliconcontrolled rectifiers each having gate and anode electrodes, and acathode electrode connected to s negative terminal, connecting saidfirst and rd larnps betwee said anode electrode of said first rectifierand said positive terminal, means connecting said second and fourthlamps between said anode electrode of said second rectifier and saidpositive terminal, a commutating capacitor connected between said anodeelectrodes, and means for periodically applying a pair of synchronizedpulses to said gate electrodes to initiate conduction of one rectifierand thereby cut oil conduction through the other.

References Cited in the file of this patent UNITED STATES PATENTS2,891,195 Srnyth June 16, 1959 3,002,127 Grontlrowski Sept. 26, 19613,024,386 Chauvineau Mar. 6, 1962

14. IN A RAILROAD FLASHING LIGHT SYSTEM, NEGATIVE AND POSITIVE TERMINALSFOR CONNECTION TO A VOLTAGE SOURCE, FIRST AND SECOND SILICON CONTROLLEDRECTIFIERS EACH HAVING GATE AND ANODE ELECTRODES, AND A CATHODECONNECTED TO SAID NEGATIVE TERMINAL, FIRST AND SECOND LAMPS RESPECTIVELYCONNECTED BETWEEN SAID ANODE ELECTRODES AND SAID POSITIVE TERMINAL, ACOMMUTATING CAPACITOR CONNECTED BETWEEN SAID ANODE ELECTRODES, MEANSNORMALLY OPERATIVE TO MAINTAIN EACH OF SAID GATE ELECTRODES AT A CERTAINPOTENTIAL RELATIVE TO SAID CATHODE, MEANS FOR PERIODICALLY APPLYING APAIR OF SYNCHRONIZED PULSES TO SAID GATE ELECTRODES TO INITIATECONDUCTION OF ONE RECTIFIER AND THEREBY CUT OFF CONDUCTION THROUGH THEOTHER, AND A PAIR OF RESISTORS CONNECTED IN PARALLEL WITH SAIDRECTIFIERS TO REDUCE THE VOLTAGE ACROSS EACH RECTIFIER WHILE IT ISNON-CONDUCTIVE AND TO ALSO MAINTAIN THE ASSOCIATED LAMP IN A DIMMEDCONDITION.